Superabsorbent polymers can be employed in various applications, such as in disposable sanitary products (i.e. diapers, incontinence articles, feminine hygiene products, and absorbent dressings), airlaids, household articles, sealing materials, humectants (i.e. agricultural products for soil conditioning), mining and oil drilling, anti-condensation coatings, water-storing materials (for use in fields as diverse as agriculture, horticulture and forestry), absorbent paper products, surgical absorbents, pet litter, bandages, wound dressings, chemical absorbents, polymeric gels for cosmetics and pharmaceuticals, artificial snow, in fire-fighting techniques, and in applications related to the transportation of fresh food or seafood, as well as in food packaging applications.
The largest use of superabsorbent materials or polymers (also referred to as SAP), however, is in disposable personal hygiene products. These products include, in the order of volume of superabsorbent materials used, diapers, training pants, adult incontinence products and feminine hygiene products.
Superabsorbent polymers and fluff cellulose pulp are usually mixed uniformly in diapers and incontinence products. This mixture of fluff and superabsorbents is formed in absorbent structures called “absorbent cores”. Unfortunately, physiological fluids are excreted and absorbed over only a small area of these absorbent cores. The superabsorbent performance of these absorbent cores is therefore not optimal.
Fluid acquisition or fluid distribution layers have been added to diapers and incontinence garments for some time. (See, for example, U.S. Pat. No. 5,137,600 (Barnes et al).) These nonwoven textiles increase liquid diffusion along the length and width of absorbent structures (i.e., along the X and Y axes), and in this way increase the amount of superabsorbents that is placed in contact with fluids. However, nonwoven textiles do not enhance the performance of superabsorbents. Nonwoven textiles can only be placed at the surface of absorbent structures, and this minimizes their impact on liquid penetration through the absorbent structures (i.e., along the Z axis). Furthermore, they are usually very expensive. Due to their high cost, fluid distribution layers are usually placed over a small area in absorbent structures and thus have only a limited effect on liquid diffusion.
Superabsorbent polymers (SAP) can be mixed with inorganic additives, such as clays, zeolites or silicates. Several additives have been mixed with superabsorbent polymers or in hygiene products for odor control purposes. (See, for example, U.S. Pat. No. 6,225,524 and European Patent No. 0751 791 (Guarracino et al); U.S. Pat. No. 6,096,299; International Patent Application No. WO 91/12031 (Ryan et al); International Patent Application Nos. WO 99/30754 and 99/30752 (Carlucci et al); U.S. Pat. No. 5,980,879 (Hiroki et al); Japanese Patent No. 04-114741 (Takahashi et al); U.S. Pat. No. 6,175,055 (Schöne); International Patent Application No. WO 91/11977 (Furio et al); International Patent Application No. WO 81/01643 (Dodwel et al) and U.S. Pat. No. 4,826,497 (Marcus et al). However, not all of these additives were reported to improve superabsorbent performance in diapers or incontinence garments.
Wong et al (United States Patent Application No. 2003/131,799), Brehm et al (United States Patent Application No. 2003/158,296 and U.S. Pat. No. 5,248,709) and Brüggeman et al (U.S. Pat. Nos. 5,847,031 and 5,721,295) describe absorbent polymer compositions made from matrix bound (melt bound) particles of superabsorbent polymers and additives. The additives are either polysaccharides or clays. As described in Pietsch (Agglomeration Processes: Phenomena, Technologies, Equipment, Wiley-VCH, 2002, ISBN 3-527-30369-3, at page 44), matrix forming binder components fill entire pore spaces, and therefore drastically reduce porosity and accessible surface area. High specific surface areas and porosity provide higher driving forces for fluid transport through the absorbent structure, as demonstrated by Roe (U.S. Pat. No. 5,419,956).
Superabsorbent material was also reported to play a role as a matrix material or binder. Hiroki et al (U.S. Pat. No. 5,980,879) teaches that superabsorbent particles occlude odor control additives, such as zeolites. Jiro et al (Japanese Patent No. 59-008711) and Herfert et al (United States Patent Application No. 2005/239,942) describe superabsorbent particles that occlude additives, such as clays, alumina or silica. Suskind et al (U.S. Pat. Nos. 5,539,019 and 5,849,816) discuss solid cores covered with absorbent polymers. Murukami et al (U.S. Pat. No. 4,418,163) and Herfert et al (United States Patent Application No. 2005/245,393) are concerned with superabsorbents coated with inorganic particles (clay, calcium carbonate, magnesium silicate, barium sulphate). Kobayashi et al (U.S. Pat. No. 5,489,469) and Sears (U.S. Pat. No. 6,855,182) describe composites made from fibers, swollen absorbent polymers and water insoluble inorganic materials, such as alumina, silica, zeolite and clays. The absorbent materials will therefore fill pore spaces, drastically reducing accessible surface area.
Takahashi et al (Japanese Patent No. 04-114741), Chmelir et al (European Patent No. 0318989), Obayashi et al (U.S. Pat. No. 4,732,968), Yanagisawa et al (Japanese Patent No. 08-010616) and Woodrum et al (U.S. Pat. No. 4,914,066) report agglomerated particles made from silicates and fine superabsorbent particles. Takai et al (U.S. Pat. No. 6,284,362) is concerned with agglomerated particles made from metal oxides and fine superabsorbent particles. Reeves et al (U.S. Pat. No. 6,387,495), Skidmore et al (International Patent Application No. WO 00/16816), Luke et al (U.S. Pat. No. 5,609,123) and Toth et al (U.S. Pat. No. 5,339,769) teach agglomerated particles made from clays and fine superabsorbent particles. Yen et al (U.S. Pat. No. 3,900,378) describe agglomerated particles made from diatomaceous earth, clay or magnesium silicate and fine superabsorbent particles. As reported by Berg et al (U.S. Pat. No. 5,300,565) water-agglomerated superabsorbent fine particles dissociate upon contact and/or swelling with an aqueous solution. This results in a concentration of swollen free fine particles that will contribute to an increased gel blocking.
McKinley et al (U.S. Pat. No. 4,500,670), Duchane (U.S. Pat. No. 3,932,322) and Tsubakimoto et al (U.S. Pat. Nos. 4,734,478 and 4,286,082) describe optimized superabsorbents mixed with additives, such as silica, diatomaceous earth and clays. As discussed in Roe (U.S. Pat. No. 5,419,956), none of the foregoing appears to have adequately understood and addressed the problems associated with the transport rate of fluids in both the X-Y plane and in the Z-direction. Moreover, these additives are not made from organic components.
Kodaira et al (Japanese Patent No. 01-004653) and Sun et al (U.S. Pat. No. 6,124,391) report superabsorbent compositions comprising inorganic substances, especially kaolin. Sun emphasizes anti-caking effects of inorganic substances, but also demonstrates improved SAP performances attributed to the inorganic component. However, Sun and Kodaira don't describe additives made from organic components.
Biodegradability and sustainable development issues were raised recently in the superabsorbent industry when increases in oil prices created provisioning problems (Kuster B., Nonwovens World, December-January 2005, p. 57). One solution to the “SAP shortage” was to propose a reduction of the SAP content in hygiene articles. However, this strategy does not necessarily involve SAP optimization.
As alternatives, the Groupe Lysac proposed many absorbent compositions made from biodegradable and renewable feedstocks. (See, for example, Canadian Patent No. 2,308,537 (Huppé et al); Canadian Patent No. 2,362,006 (Couture et al); Canadian Patent No. 2,426,478 (Bergeron); Canadian Patent No. 2,462,053 (Thibodeau et al; and Canadian Patent No. 2,483,049 (Berrada et al).) However, these patents do not relate to additives that have the effect of improving the performance of superabsorbents.
Takahiro et al (Japanese Patent No. 01-296933), Marx (U.S. Pat. No. 4,615,923) and Brander et al (U.S. Pat. No. 6,376,034) describe inorganic additives (kieselguhr, clays, diatomaceous earth) added to biodegradable superabsorbents. However, none of these patents teach additives made from organic components.
Richman et al (U.S. Pat. No. 4,454,055) and Spence (U.S. Pat. No. 4,272,514) report the use of starch, a natural and biodegradable polymer, as an additive for superabsorbent polymers. Richman and Spence also teach the use of inorganic additives for enhancing the performance of superabsorbent polymers. However, neither Richman nor Spence describes the use of both organic (starch) and inorganic components in a single particle.
There thus remains a need for an additive that effectively improves the performance of superabsorbents. Ideally, such an additive would be cost-efficient and be composed of mainly renewable resources. Moreover, the additive would combine synergistically, in a single particle, organic components as well as inorganic components.
The present invention seeks to meet these and other needs.
The following description refers to a number of documents, the contents of which are herein incorporated by reference in their entirety.